An apparatus of the type described above is known from DE-GM 91 09 180.2. In the area of a screw conveyor device with a shaft arranged horizontally, i.e. lying down, the raked-off material, which has been separated by another device, is fed via a feed hopper into the screw conveyor device. It moves into a pre-compacting zone which is provided between feed hopper and washing zone. In the compacting zone, the shaft is constructed without a conveyor helix so that here the raked-off material fills the whole cross-section of the conveyor device and is compressed. In the subsequent mixing and washing zone, the shaft of the screw conveyor device has no conveyor helix, instead several axial mixing blades are located on the shaft and distributed over the circumference, and these brush over almost the entire open cross-section of the housing. The mixing blades can be attached to the shaft of the screw conveyor device at a pitch. They can be designed as segmental pieces. Connected downstream of the mixing and washing zone is a rising discharge pipe so that a second compacting zone is formed here. The wall of the housing for the complete screw conveyor device is provided with openings in the lower region, through which the wash water drains. The lumps of raked-off material, formed in the initial compacting zone, are broken down and crushed by the mixing blades in the mixing and washing zone, whereby the soluble, organically degradable constituents contained therein are washed out by the wash water. The disadvantage here is the breaking-down of the raked-off material and the inadequate degree of washing out because the wash water escapes unhindered through the openings in the walls of the housing so that a nominal water level cannot be built up. The use of mixing blades projecting more or less radially from the shaft brings with it the danger that raked-off material can settle on these blades and become stuck there. In particular, with the accumulation of more raked-off material, fed via the screw conveyor device and through the first compacting zone, there is the possibility that the washing zone clogs up. Interruptions to the operation are the consequence.
De-OS 37 15 019 demonstrates an apparatus for separating solid matter from fluids, in particular for separating sewage sludge. The raked-off material with the adhering faecal matter, which has been separated in another device, is fed to the separator which is constructed as a screw conveyor device with an axis arranged at an angle. The driven shaft has a continuous conveyor helix; a gap is formed between the edge of said conveyor helix and the inside wall of the housing. Washer nozzles are provided in the middle section of the axial length of the housing and these feed wash water into the inside of the apparatus. The gap between the conveyor helix and the housing becomes more or less closed off depending on the amount of the raked-off material present so that the raked-off material is enclosed by the wash water in the area of each conveyor helix and the nozzles spray onto the surface of the water so that the wash-out effect is correspondingly low.
An apparatus for removing raked-off material from fluid flowing in a channel in a sewage treatment plant is known from DE-OS 40 42 167 in which a washing zone is realized following the separator. The screw conveyor device extending through the separator and the washing zone is arranged with an axis at an angle. The shaft of the screw conveyor device supports a conveyor helix which extends through the washing zone and only ends before the compacting zone. In the area of the washing zone, washer nozzles are arranged over the axial length as well as distributed over the periphery so that wash water can be sprayed onto the contaminated raked-off material using these washer nozzles. Cropping and conveying blades, fixed on the internal periphery of the housing walls, extend throughout the washing zone so that appropriate discharge channels for the drainage of the wash water ensue between the edge of the conveyor helix and the housing. A nominal water level cannot build up here in the washing zone, instead the main washing effect is achieved through the spraying of wash water onto the raked-off material and the corresponding mixing and rearranging within the raked-off material which is already made available through the conveying effect of the screw conveyor device.